To my surprise the ICO claim to be unable to play a call recording. I have sent them details of junk calls, as a simple WAV file. I offered to send as MP3 in future, but they say they are unable to play an audio file.
I have to wonder what sort of IT kit they have that is unable to play such a file!
They also want me to tell them what is in the call recording and so on.
I have pointed out that, unlike them, I am not paid to enforce this legislation, my time is valuable. Sending the call recording with date/time and numbers gives them all the evidence in the most efficient way for me (the victim of the crime).
I'll keep sending them until they get the necessary IT to be able to play a recording. After all the law says I can ask them to exercise their enforcement action, and that is all I am doing. If they don't like that they can get the law changed. It is not like I am spamming them. I'll try MP3 files anyway, we'll see.